The present invention relates generally to semiconductor lasers. More particularly, the present invention relates to modulation of semiconductor lasers.
Semiconductor lasers have become more important. One of the most important applications of semiconductor lasers is in communication systems where fiber optic communication media is employed. With growth in electronic communication, communication speed has become more important in order to increase data bandwidth in electronic communication systems. Improved semiconductor lasers can play a vital roll in increasing data bandwidth in communication systems using fiber optic communication media such as local area networks (LANs), metropolitan area networks (MANs) and wide area networks (WANs). A preferred component for optical interconnection of electronic components and systems via optical fibers is a semiconductor laser.
One type of well known semiconductor laser is a vertical cavity surface emitting laser (VCSEL). The current state of design and operation of VCSELs is well known. Due to optical properties of optical fibers, photons emitted at longer wavelengths from a laser tend to propagate longer distances and are less disturbed by optical noise sources. Thus, forming a VCSEL that can operate at longer wavelengths, such as a wavelength greater than 1.25 xcexcm, is desirable.
Lasers can be excited or pumped in a number of ways. Typically, VCSELs have been electrically excited (i.e. electrically pumped) by a power supply in order to stimulate photon emission. However, achieving photon emission at long wavelengths using electrical pumping has not been commercially successful due to a number of disadvantages. More recently it has been shown that a VCSEL can be optically excited (i.e. optically pumped) to stimulate photon emission.
In order to use a semiconductor laser in communication systems, the laser output needs to be modulated somehow to communicate a signal. One type of laser modulation scheme varies the intensity of the light generated by the laser. Oftentimes this has been done externally from the laser, similar to a camera""s shutter allowing light to pass through to an unexposed film. However, this requires additional elements. It is more desirable to directly modulate a semiconductor laser. However previously, direct modulation of semiconductor lasers at the desired high frequencies of communication systems has been limited by jitter and chirping in addition to turn-on delays. Turn-on delay is the time it takes for a semiconductor laser to emit photons in response to receiving an electric turn on signal. Jitter refers to the variations in the pulses of emitted photons in relation to a constant pulse train of an electric signal. Chirping refers to changes in the wavelengths of the emitted photons from a semiconductor laser.
It is desirable to overcome the limitations of the prior art.
Briefly, the present invention includes methods, apparatus and systems as described in the claims.
Modulated integrated optically pumped vertical cavity surface emitting lasers are formed by integrating an electrically pumped semiconductor laser and a vertical cavity surface emitting laser (VCSEL) together with a means of direct modulation of the electrically pumped semiconductor laser. In the preferred embodiments, the electrically pumped semiconductor laser is a type of folded cavity surface emitting laser (FCSEL). In a number of embodiments, the FCSEL is partitioned into two sections by a gap in material layers. In these embodiments, one section of the FCSEL is biased so as to maintain the generation of photons without causing the optically pumped VCSEL to lase while the second section of the FCSEL is used for modulation and causes the optically pumped VCSEL to lase. In another embodiment, an electric-absorption modulator is sandwiched between an electrically pumped FCSEL and an optically pumped VCSEL. The electric-absorption modulator acts similar to a camera shutter and allows photons to pass through from the electrically pumped FCSEL to the optically pumped VCSEL when in one state and blocks photons from reaching the optically pumped VCSEL when in another state.